The present invention relates to a hot rolling method for metal blocks, and more particularly, relates to a metal block hot rolling method for joining several to several tens of metal blocks, such as sheet bars, slabs, billets, or blooms, and subjecting the metal blocks to continuous rolling.
In a conventional metal block hot rolling line, metal blocks to be rolled are individually subjected to heating, rough-rolling, and finish-rolling, and are finished as hot-rolled strips having a desired thickness. In such a batch rolling method, however, the line is inevitably stopped due to poor biting of rolled materials. Moreover, the yield is significantly decreased due to odd shapes of the leading end and the tail end of the rolled materials.
For this reason, an endless rolling method has been recently adopted in which the tail end and the leading end of metal blocks to be rolled are coupled (hereinafter referred to as xe2x80x9cjoinedxe2x80x9d) in advance of finish-rolling, and the metal blocks are continuously supplied to a hot rolling line so as to be rolled.
In such endless rolling, since the poor biting and the odd shapes described above occur only at the leading end of the first and the tail end of the last of a plurality of joined subsequent metal blocks, such can be greatly reduced. Since the poor biting and odd shapes become more likely to arise as the thickness of the finish-rolled strips decreases, there used to be such problems in the conventional batch rolling method, and the producible thickness of rolled strips used to have a lower limit. In endless rolling, however, a thick metal strip is rolled first, next the thickness of the finish-rolled strip is changed during rolling after the leading end of the thick strip threads through a finish-rolling unit, and then the subsequent thin metal strips are rolled, so it can produce thinner gage rolled products than before.
As a hot rolling system that can perform the above-described endless rolling, for example, Japanese Unexamined Patent Publication No. 7-241601 discloses a hot rolling line in which arranged, in order along the line on the outlet side of a heating furnace 20, are a rough-rolling unit 22 composed of, for example, three stands R1 to R3, a winding and rewinding device 70, a leveler 72, a centering guide 74, a joining crop shear 30, a movable joining unit (welder) 40 moving in synchronization with the feeding of metal blocks, a crop shear 24, a finish-rolling unit 26 composed of, for example, seven stands F1 to F7, and, for example, two coilers 28 for alternately coiling, as shown in FIG. 2.
Japanese Unexamined Patent Publication No. 7-1007 discloses an example of a movable joining unit, in which plural lifting table rollers 66 to be supplied with balanced oil pressure from hydraulic oil pipes connected uniquely are pressed down by guides 45A and 45B mounted on a joining unit 40 and are raised by the balanced oil pressure to the initial metal block supporting height in accordance with the traveling of the joining unit, as shown in FIG. 3, thereby preventing the table rollers and the joining unit from colliding with each other.
Japanese Unexamined Patent Publication No. 11-169926 discloses a method in which, in order to prevent operating trouble or defective coils due to inaccurate setting change and delay of setting change, by promptly and accurately changing the settings when endless rolling for joining and rolling a preceding metal block and a succeeding metal block is changed to batch rolling for rolling a preceding metal block and a succeeding metal block without joining, both rolling conditions of endless rolling and conditions of batch rolling are predetermined when slabs are subjected to endless rolling, and operating conditions at each point in a hot rolling line are calculated for both endless rolling and batch rolling.
However, measures to be taken when trouble arises in an actual joining operation in such a continuous hot rolling line have not been hitherto specifically disclosed. If there are no measures to be taken in case of trouble, serious trouble may arise.
In general, materials (a preceding metal block 10 and a succeeding metal block 12) are pushed upward from below by loopers 16 during finish rolling, as shown in FIG. 4, in order to apply tension to the materials between the stands. For example, if the unjoined materials are supplied to the finish-rolling unit 26 with a false determination that the materials have been joined, since the loopers 16 between the stands are keeping the materials in an upward position, as shown in FIG. 7, the leading end of the succeeding metal block is flipped up by the looper 16, is not bitten by the next stand, and jams between the stands. Thereby, the rolling operation cannot be continued, and the operation of the line is stopped.
Similarly, in a case in which although a joint 11 between the tail end 10B of the preceding metal block and the leading end of the succeeding metal block 12A is incomplete and has an insufficient strength, as shown in FIG. 5, it is subjected to finish rolling with a false determination that the joint is complete, as shown in FIG. 6, the joint 11 may be broken by tensile force, the leading end of the succeeding metal block 12A is flipped up by the looper 16, is not bitten by the next stand, and jams between the stands, as shown in FIG. 7. Due to this, the rolling operation cannot be continued, and the operation of the line is stopped. Numeral 14 in FIG. 6 denotes burrs produced by joining.
There are three basic trouble cases, as follows:
(1) It is impossible to start joining metal blocks.
(2) Joining results in failure due to trouble during the joining operation.
(3) Although a joint is formed, it has low strength and is incomplete.
The present invention has been made to overcome the above-described conventional problems, and an object of the present invention is how to deal with the above three trouble cases.
This invention solves the above problems by a hot rolling method for metal blocks using a hot rolling system for joining the leading end of a succeeding metal block and the tail end of a preceding metal block on the inlet side of a finish-rolling mill and for finish-rolling the succeeding metal block and the preceding metal block continuously. In this method, it is determined before, during, and after the joining operation whether or not the succeeding metal block can be finish-rolled in succession to the preceding metal block. When it is determined that the succeeding metal block cannot be finish-rolled in succession to the preceding metal block, the joining operation is aborted or a joint is cut, and rolling operations (operations concerned with all the devices placed downstream from a joining unit, such as finish rolling, coiling, and run-out cooling) are performed in downstream devices including the joining unit under the conditions set for batch rolling. FIGS. 37(a) and 37(b) show the positional relationship among a preceding metal block 10, a succeeding metal block 12, a subsequent metal block 13, and a cut joint, when the joining operation is aborted, and when the joint is cut, respectively (Invention 1).
Regarding the succeeding metal block that is not joined or is incompletely joined, if the devices (the joining unit and a treatment unit such as a deburring device) concerned with joining remain in a joining state, the leading end of the succeeding metal block that is not joined or that the incomplete joint resulted in being broken during traveling, after the joining operation is aborted, is at a risk of sticking in the interior of the devices concerned with joining and making it impossible for the leading end of the succeeding metal block to be threaded therethrough. Accordingly, the devices are brought into a state that allows the leading end of the succeeding metal block to be threaded therethrough, and the leading end of the succeeding metal block is then threaded through the devices concerned with joining. That is, according to this invention, the above problems are solved by the hot rolling method for metal blocks is using a hot rolling system for joining the leading end of a succeeding metal block to the tail end of a preceding metal block on the inlet side of a finish-rolling mill and for finish-rolling the succeeding metal block and the preceding metal block continuously. In this method, when it is determined that the succeeding metal block cannot be finish-rolled in succession to the preceding metal block, an operation of joining the leading end of the succeeding metal block and the tail end of the preceding metal block is aborted when the metal blocks are separate. When the metal blocks are joined incompletely, a region including a joint therebetween is cut between the joining unit and a finish-rolling mill, the downstream devices for joining including the joining unit are brought into a state that allows the leading end of the succeeding metal block to be threaded therethrough, and at least the leading end of the succeeding metal block is bitten by the finish-rolling mill set for batch rolling (Invention 2).
According to this invention, when it is determined, before joining, that the succeeding metal block cannot be finish-rolled in succession to the preceding metal block, the joining devices are brought into a state that allows the leading end of the succeeding metal block to be threaded therethrough. After the tail end of the preceding metal block moves out of the finish-rolling mill, a setting of the finish-rolling mill is made for batch rolling so that the leading end of the succeeding metal block is bitten by the finish-rolling mill. Subsequently, the leading end of the succeeding metal block is threaded through the joining devices and is bitten by the finish-rolling mill. Thereby, the above problems are solved (Invention 3).
According to this invention, after joining, it is determined, according to whether or not the joining operation was performed successfully, whether or not the succeeding metal block and the preceding metal block can be finish-rolled in succession. When it is determined that the joining operation was not performed successfully, a region including the joint therebetween is cut between the joining unit and the finish-rolling mill, and at least the leading end of the succeeding metal block is bitten by the finish-rolling mill set for batch rolling. Thereby, the above problems are solved. In this case, it is preferable that the devices disposed on the feeding path from the joining unit to a joint cutting means be placed in a state that allows the leading end of the succeeding metal block to be threaded therethrough so that the leading end is prevented from sticking and stopping even when the joint is broken during feeding (Invention 4).
In this invention, the joint between the preceding metal block and the succeeding metal block incompletely joined may be fed in synchronized velocity with the travel of the joining unit, the joining unit may travel and stop at the most downstream end of the travel zone, and the preceding metal block and the succeeding metal block may be continuously fed, without being stopped, at the feeding speed of the preceding metal block whose leading end has been already rolled by the finish-rolling mill (Invention 5).
In general, endless rolling adopts an operation manner in which the leading end of the first metal strip in endless rolling is rolled to a somewhat larger thickness so as to be threaded through the finish-rolling mill, the traveling sheet thickness in the finish-rolling mill is changed after the leading end has been threaded through the finish-rolling mill, and thin metal strips are rolled. Therefore, joining of the leading ends of the second and subsequent metal blocks in endless rolling is aborted, or the leading ends are bitten by the finish-rolling mill after the incomplete joint is cut. That is, when the leading end is subjected to batch rolling, the target finishing thickness is too small, and the threading ability is unstable, which may make rolling impossible. On the assumption of such a case, a thickness range that allows batch rolling is preset. When the target finishing thickness of the succeeding metal strip is out of the thickness range, finish rolling is performed while the finishing thickness of at least the leading end of the succeeding metal strip is changed to be within the thickness range. In this case, even if the target thickness of the succeeding metal strip, which has been aborted to be joined to the preceding metal block, is small, the thickness at the leading end is changed to be larger, and the succeeding metal strip is bitten by the finish-rolling mill, which achieves stable finish rolling. That is, according to this invention, when it is determined that the succeeding metal block cannot be finish-rolled in succession to the preceding metal block, the finishing thickness range that allows batch rolling is preset, and the succeeding metal block is finish-rolled with the finishing thickness of at least the leading end thereof changed to be within the thickness range when the target finishing thickness of the succeeding metal strip is out of the thickness range. Thereby, the above problems are solved (Invention 6).
According to this invention, in a case in which it is determined that the succeeding metal block cannot be finish-rolled in succession to the preceding metal block, when the joining unit is mounted on a truck and moves while the truck sequentially depressing lifting table rollers with its movement with table pressing guides on the inlet side and the outlet side of the joining device placed in the down position, and the lifting table rollers sequentially returning to the unpressed initial height state after the truck passes, the truck is stopped, after the joining operation is stopped or is finished incompletely, at a position such that the distance Q between the table rollers and the outermost one of feeding rolls provided with the truck prevents the succeeding metal block from entering between the rolls due to downward bending while the outlet-side table pressing guide is in the upper limit position. Then, the outlet-side table pressing guide is raised to the upper limit position, and the succeeding metal block or the joint is fed downstream from the joining unit. Thereby, the above problems are solved.
Furthermore, according to this invention, when the incomplete joint is fed downstream from the joining unit, even if separated, the joining unit is stopped at a position such that the gap between adjacent table rollers prevents the leading end of the succeeding metal block, after separating, from bending downward and from entering between the table rolls. Then, at least the table pressing guide on the downstream side (on the outlet side of the joining unit) is raised, and the preceding metal block and the succeeding metal block are not stopped, but are fed at the feeding speed of the preceding metal block whose leading end has been already rolled by the finish-rolling mill (Invention 7).
According to this invention, when the joining unit clamps the succeeding metal block and the preceding metal block with a predetermined gap formed between the leading end of the succeeding metal block and the tail end of the preceding metal block, heats the leading end and the tail end in this state, and joins the leading end and the tail end by pressing, it is determined, based on the amount of displacement by pressing, whether or not joining has been successfully performed (Invention 8).
According to this invention, it is determined before, during, and after joining whether or not the succeeding metal block can be finish-rolled in succession to the preceding metal block. When it is determined that it is impossible, a treatment unit disposed between the joining unit and the finish-rolling mill so as to treat the joint is brought into a state in which the joint is not treated. The leading end of the succeeding metal block is threaded therethrough when the joining operation is aborted, and the joint is threaded therethrough when the joint is incomplete (Invention 9).
According to this invention, in a case in which a deburring device is placed on the outlet side of the joining unit so as to deburr the joint by rotary cutters, which are disposed above and below the pass line to be rotated in the opposite direction from the feeding direction of the succeeding metal block, and to remove bur produced at the joint, deburring by the deburring device is aborted when it is determined that the joining operation was not performed successfully (Invention 10).
On the other hand, the succeeding metal block bitten by the finish-rolling mill with its finishing thickness changed and a subsequent metal block subsequent to the succeeding metal block can be subjected to endless rolling while the leading end and the tail end thereof are joined, as long as no trouble arises. However, this involves conditions. Since at least the leading end of the succeeding metal block is sometimes rolled to a thicker thickness than the target finishing thickness others throughout its length, there is caused a need to unexpectedly change the traveling sheet thickness, or to change the traveling sheet thickness by a greater amount than predetermined in order to roll the succeeding metal block and the subsequent metal block in succession. If the amount of change in traveling sheet thickness is too large, shape control and the like during rolling cannot be finely performed, and it is significantly difficult to roll the portion with the changed traveling sheet thickness.
Accordingly, the present invention solves the above problems by the hot rolling method for metal strips using a hot rolling system in which the traveling sheet thickness can be changed to change the finishing thickness during finish rolling. In the method, the hot rolling system allows the traveling sheet thickness change for changing the finishing thickness during finish rolling, and a changeable thickness range in accordance with the traveling thickness change is preset. When a subsequent metal strip subsequent to the succeeding metal strip and the succeeding metal strip finish-rolled to a different thickness from the target thickness for continuous rolling are finish-rolled in succession, it is determined whether or not the amount of change in thickness from the finishing thickness of the succeeding metal strip to the target finishing thickness of the subsequent metal strip is within the changeable thickness range. When the change amount is out of the changeable thickness range, the finishing thickness of the subsequent metal strip is changed so that the amount of change in thickness be within the changeable thickness range, and the subsequent metal strip and the succeeding metal strip are joined and are subjected to continuous finish rolling. This makes it possible to roll (endless-roll) the succeeding metal strip and the subsequent metal strip in succession without any trouble even when the succeeding metal strip has been rolled to a greater thickness than the target value (Invention 11).
When the target thickness of the subsequent metal block is also achieved by batch rolling, or when none of the metal blocks to be joined can be finish-rolled to the target thickness even by sequentially joining the metal blocks from the subsequent metal block to the predetermined last block while changing the target thicknesses within the changeable traveling sheet thickness range, as described above, joining of the leading end of the subsequent metal block may preferably be aborted. This also applies to the materials subsequent to the subsequent metal block (Invention 12).